As the advance of Metal-Oxide-Semiconductor Field-Effect Transistor, MOSFET, more and more applications are implemented on a single chip. Because the frequency of transmission signal is higher following different generations, avoiding electromagnetic interference (EMI) to the transmission signal has become an issue for the industry. One approach to avoid the EMI to the transmission signal is by blocking the EMI from every possible aspect. However, the cost of using this blocking technology is high and therefore, it is often not the first choice for the industry. Another approach to prevent EMI to the signal is called spread spectrum clock, which is able to be integrated into the circuit and thus widely accepted.
Spread spectrum clock itself is a frequency modulated signal such that it is able to distribute the energy on the carrier wave to a specific band to accomplish the purpose of reducing the electromagnetic interference to the signal so transmitted. Many applications have been developed and implemented, which includes direct modulation to voltage-controlled oscillator, VCO, modulation to Delta-sigma integrator and direct generation of spread spectrum clock using open loop. All the methods mentioned above are implemented by adding modulated signal to generate spread spectrum clock. However, using Delta-sigma modulator to achieve frequency synthesis increases noises in the device, it also consumes more power. None of the above can avoid complex design, large power consumption and large area so required for the purpose.
In order to solve the problem(s), the present invention introduces a circuit which is able to reduce noise in the device and can be implemented in a small area.